Microcephaly Was Endemic in Brazilian Cities Prior to 2015 Zika Outbreak

Microcephaly underreported by 90% before Zika epidemic in Brazil

new born baby being born

New research found that Brazil ‘grossly’ underestimated the number of microcephaly cases prior to the introduction of the Zika virus epidemic in 2015.

Researchers estimate that nearly 90% of microcephaly cases before the epidemic were not reported.

The prevalence of severe microcephaly was found to be much higher than expected in two municipalities, before the circulation of the Zika virus, according to this new study published in Pediatrics

“The Zika virus was first noticed in Brazil in May 2015. Shortly thereafter, an increasing notification of microcephaly at birth was reported, and a possible link with the Zika virus was announced,” Antônio A. Silva, MD, Ph.D., from the Federal University of Maranhão, São Luís, Brazil, and colleagues wrote.

To evaluate the prevalence of microcephaly within two Brazilian cities and the risk factors associated with the condition before the Zika outbreak, Dr. Silva and colleagues used population-based data from the Brazilian Ribeirão Preto and São Luís birth cohort studies of 2010, that included hospital deliveries by resident mothers.

These researchers reported their findings were confined to a few geographical areas, and are not population based in Brazil.

Microcephaly at birth was classified according to the criteria of the International Fetal and Newborn Growth Consortium for the 21st Century and the Brazilian Ministry of Health.

Risk factors for microcephaly included low maternal education level, living in a consensual union or without a companion, maternal smoking during pregnancy, primiparity, vaginal delivery and intrauterine growth restriction.

To avoid a repeat of this under-reporting, these researchers offered this recommendation.

“In view of the severity of the Zika epidemic, it is highly advisable that countries set up head circumference monitoring systems to detect early signs of this (microcephaly) syndrome,” Dr. Silva and colleagues wrote.


This new study is in contrast to a previous study by Dr. Leonelo Bautista, which was published in the December 2017 edition of the journal Annals of Epidemiology.

Dr. Bautista found that babies of Zika-infected mothers didn’t have significantly more microcephaly.

One factor that made it seem like there was a spike in microcephaly cases in 2015 was that criteria for the condition changed that year to include children with larger heads than before. And, that studies suggesting a link between Zika and microcephaly, were too small to draw conclusions, he said.

According to the Center for Disease Control and Prevention (CDC), Microcephaly is a congenital malformation resulting in smaller than normal head size than expected as compared to infants of the same age (or gestational age) and sex.

It has also been associated with other birth defects and neurologic conditions in children and adults.

For infants diagnosed with microcephaly, head size correlates with underlying brain size. Microcephaly is defined as occipitofrontal circumference less than the third percentile, based on standard growth charts for sex, age, and gestational age at birth.

However, these measurements do not consistently predict long-term sequelae. Neurologic sequelae may include seizures, vision or hearing problems, and developmental disabilities. Symptoms vary with the extent of brain disruption.

Babies can develop microcephaly after birth if their head growth slows or fails to develop. There have been no reports of Zika virus infection around the time of birth leading to microcephaly in infants.

Disclosures: The authors report no relevant financial disclosures: Antônio A. Silva, Marco A. Barbieri, Maria T. Alves, Carolina A. Carvalho, Rosângela F. Batista, Marizélia R. Ribeiro,Fernando Lamy-Filho, Zeni C. Lamy, Viviane C. Cardoso, Ricardo C. Cavalli, Vanda M. Simões, Heloisa Bettiol.